Conventionally, on large transport aircraft aerodynamic control surfaces, such as spoilers, are attached to a corresponding aircraft structure by means of primary hinges, failsafe hinges and drop links. Specific construction techniques have been developed for the installation of such control surfaces, specifically to provide the desired operating and failsafe characteristics of the aircraft component.
The following description is specifically provided in the context of providing failsafe functionality to spoiler installations. However, it is to be understood that this example of the invention has been chosen as it provides particular descriptive clarity. The present invention may be equally applied, with appropriate modification, to control surfaces in general such as ailerons, elevator and vertical tail plane.
An example of a spoiler construction is shown in FIG. 1 which illustrates a spoiler installation for the Airbus A380 civil passenger aircraft. The remainder of the wing structure is omitted for clarity. According to the illustrated example, primary hinges C and D are located on the trailing edge of corresponding spoiler ribs 13a and 13b. The spoiler ribs are mounted on the trailing edge of the wing box (not shown).
Spoiler 10 is mounted on hinges C and D by means of the hinge construction indicated generally by the numerals 19 and 100 respectively. These primary hinges are the main load-bearing components that support the spoiler 10 and react to the aerodynamic forces created when the spoilers are extended. Drop links generally indicated by the numeral 32, are located at either end of the spoiler 10 where the spoiler engages with the wing trailing edge structure. FIG. 2 illustrates details of a conventional droplink at an intermediate position where the spoiler is attached to a spoiler rib 15. Referring to FIG. 2, the drop link 18 is an elongate member pivotally connected at each end 20 and 21 to the wing structure 15 and to the leading edge 14 of the spoiler 10 respectively.
Drop links serve to transmit load between the wing structure and the spoiler, whilst at the same time permitting the spoiler to conform to the shape of the wing as it bends under a range of flight loads. The ability of the droplink to rotate in a span wise direction significantly reduces the loads that would be introduced into the spoiler, hinge and wing structure if the spoiler were forced to bend in its plane of maximum stiffness when deployed, as it would be if the hinge were a simple bearing and pin arrangement as used for the main hinges.
Referring to the conventional drop link shown in detail in FIG. 2, the lower end 21 of the drop link 18 is connected by means of a spherical bearing 25 to a spoiler clevis 17. At its upper end 20, the drop link 18 is connected to the wing-box trailing edge rib structure 15, by means of a spherical bearing (not indicated). The spherical bearings allow the spoiler to pivot around the hinge axis of the spigot pin 22 as the spoiler 10 is extended and retracted, while simultaneously constraining spoiler movement in the plane defined by this rotation. Thus, with reference to FIG. 1, as the wing structure 15 moves under the action of wing flex, the drop link transmits this movement into the spoiler 10 by means of the drop link arm length. As noted above, the spoiler hinge rotation axis coincides with the lengthwise axis of drop link spigot pin 22, thus allowing simultaneous extension/retraction and bending of the spoiler depending on how far the spoiler is extended. For example, if the spoiler is fully extended, the bending force will be nearly zero as the vertical component of the drop link arm length resolved in the span wise wing direction would be small. This avoids stressing the extended spoiler due to wing flex.
One of the sources of structural failure in aircraft control surfaces is failure of their primary hinge assemblies. With reference to the present example, this corresponds to failure of the primary hinge subassembly C and D in FIG. 1. This may occur either by way of failure of the primary hinge pin 106a and/or 106b or by failure of the hinge subassembly as a whole.
Referring to FIG. 6, the location of the inboard spoilers on the wing 71 is indicated by the numeral 72 and the outboard spoilers by the numeral 73. The spoiler installation in this example includes three individual inboard spoilers 72 attached by means of primary hinges and drop links.
If a primary hinge of an inboard spoiler 72 fails under flight loads, there is a risk that the spoiler can detach and, moving in the direction indicated by the letter “A”, strike the horizontal stabilizer 74. A particularly vulnerable part of the horizontal stabilizer 74 is the leading edge 75. The impact of the spoiler 72 traveling at flight speeds can cause failure of the horizontal stabilizer 74 either by degrading its aerodynamic function or by complete catastrophic failure of the horizontal stabilizer. In either case, this damage can render the aircraft uncontrollable. Although the probability of such structural failure in a spoiler is very small, it is nevertheless finite and, over the expected lifetime of an aircraft in service, is at a level, which, without a failsafe system, is unacceptable in civil aircraft production.
To reduce this failure probability, spoiler failsafe hinges are used. In the prior art example shown in FIG. 1, failsafe hinges B and E are located at intermediate positions between the primary hinges C and D.
Failsafe hinges 102a and 102b are mounted on the aft portions of correspondingly located spoiler ribs 11a and 11b. Spoiler ribs are wing ribs extending from the trailing edge of the wing box (35 in FIG. 3) to which are mounted the spoiler subassembly 10 including the hydraulic actuators, mounts and related hardware (not shown in FIG. 1).
Failsafe hinges 102a and 102b are essentially similar to the primary hinges 106a and 106b except that the failsafe hinge apertures have a diameter greater than the failsafe clevis pins. This can be seen in FIG. 8, which includes a cross-section view through a failsafe hinge. A conventional spoiler failsafe hinge part includes an apertured tab 81, which engages with spoiler clevis 101a and 101b by means of a clevis pin 80. The size of the aperture in the spoiler tab 81 is however significantly larger than the external diameter of the failsafe spoiler clevis pin 80. This can be seen by the presence of the annular void 82 (unshaded) in FIG. 1. Thus, during normal flight, no loads are applied to the failsafe clevis pin assembly. In contrast, detail of a primary spoiler hinge is shown in FIG. 7. Here a spoiler hinge includes a spoiler clevis 19, spoiler clevis pin 106b and a hinge bush 90.
If a primary hinge fails, for example, by the main hinge pin 106b or the clevis 19 failing under flight loads, the spoiler 10 displaces from its operational position. This movement continues until the failsafe hinge clevis pin 80 (see FIG. 8) contacts the inner part of the failsafe clevis 101a. In FIG. 8 this would be manifested by the hinge failsafe pin 80 moving rightwards until it bears against the inner surface of the failsafe spoiler clevis aperture 82. The spoiler 10 is thereby prevented from detaching completely from the wing structure. The overall operation of the spoiler is preserved in that the spoiler failsafe hinge allows spoiler movement through its normal range of extension and retraction without interfering with other parts of the aircraft structure or other control surfaces.
Under such conditions, although the handling of the aircraft may be affected, the probability of complete structural failure and detachment of the spoiler and the subsequent risk of horizontal stabilizer damage is reduced to an acceptable level.
One disadvantage with presently accepted spoiler failsafe hinge constructions, such as that shown in FIG. 1, and other control surface installations, is that the failsafe hinge ribs and hinges need to be present on the aircraft and reinforced appropriately. This incurs a weight penalty in the overall wing construction that is even more onerous given that it is highly unlikely that the failsafe hinge system will ever be used during the typical service life of an aircraft. However, it is a certification requirement for such a backup subassembly to be present on the wing.
The present invention attempts to address this weight penalty issue and provide an alternative control surface connection failsafe configuration.